A so-called step scroll compressor, in which step parts are provided in each of positions of tooth crests and tooth bases in spiral wraps of a stationary scroll and a revolving scroll along the spiral directions thereof, and a height of the spiral wrap on an outer peripheral side thereof is greater than a height of the wrap on an inner peripheral side thereof on the respective sides of the step parts, is capable of compressing a refrigerant gas not only in a circumferential direction of the spiral wraps but also in a wrap height direction (that is, is capable of three-dimensional compression). The step scroll compressor is thus capable of a greater amount of displacement and a higher compressor volume than a scroll compressor not provided with steps (two-dimensional compression). Accordingly, the compression ratio can be increased and the performance of the compressor can be improved without increasing the outer diameter of the compressor, and thus the compressor can be made smaller and more lightweight.
Among such step scroll compressors, Patent Document 1 discloses a step scroll compressor provided with an overcompression prevention mechanism that, when the pressure in a compression chamber rises abnormally and reaches or exceeds a set pressure before the pressure communicates with a discharge port, diverts the pressure to a discharge chamber via a bypass port and a bypass valve. On the other hand, Patent Document 2 discloses a two-dimensional compression-type scroll compressor, in which the stationary scroll and the revolving scroll have different numbers of turns, where bypass ports provided in a posterior compression chamber and an anterior compression chamber that form a pair are given different positions and sizes (numbers) in order to alleviate overcompression and liquid compression.
Additionally, Patent Document 3 discloses a horizontal scroll compressor in which a drive shaft is arranged in the horizontal direction, where at least four relief ports and one discharge port are provided between a compression chamber formed by the two scrolls and a discharge chamber, a relief valve is provided in each port, and one of the relief ports or the discharge port is configured to constantly communicate with the compression chamber. This makes it possible to prevent liquid compression and overcompression throughout the entire compression stroke.